Ethylene-based plant growth regulators (PGRs) for mitigating spring frost injuries in stone fruit species
The sustainable annual production of stone fruits in Virginia and other fruit-growing states is constantly imperiled by spring freezes. Economic losses caused by frost damage can be enormous, and the risk of frost damage is projected to rise as a result of global climate change. Global warming increases the risk of frost damage by advancing the timing of bud break and flowering and/or increasing the frequency of “false spring”, thus making frost damage a worldwide challenge in fruit production. This was reflected in a survey conducted in 2017, in which 67% of fruit growers and stakeholders in Virginia ranked the need for research on strategies to avoid or reduce frost damage in apple and peach as being important or very important. The available frost mitigation approaches (e.g., under-tree sprinklers, wind machines, helicopters, and gasoline heaters) are either ineffective, labor-intensive, economically inefficient or environmentally unsustainable. One of the avoidance mechanisms that has been suggested, yet to be accomplished, is to delay bud break and bloom date in the early-bloom species and cultivars beyond the last day of frost. Toward this goal, several studies have investigated the applicability of plant growth regulators (PGRs) as foliar applications to delay bud break. Ethylene is one of plant hormones that affects the progression, maintenance and release of bud dormancy in deciduous woody perennials, including pome and stone fruits (Figure 1). Moreover, ethylene has been used on fruit trees for decades to delay bloom and avoid frost damage. Ethephon is a plant growth regulator that degrades and releases ethylene once entering plant cytoplasm. Many studies have reported that fall application of ethephon can effectively delay the blooming time in the following spring in many fruit species, especially stone fruits (Table 1). Despite the significant success in using ethephon to delay bloom and prevent spring frost, some studies have indicated beneficial effects of ethephon can be comprised by the occurrence of detrimental effects such as gummosis, leaf yellowing and abscission, terminal dieback, flower abscission, floral bud failure, low fruit set, and yield reduction (Table 1).
Dr. Jianyang (Jay) Liu, a research associate in Dr. Sherif’s lab investigates concentrations and application timings of ethephon that can delay bloom in peach and sweet cherries cultivars. The effects of ethephon on chilling and heat requirements, leaf abscission rate, cold hardiness, bloom delay, crop yield and tree injury have been assessed in two peach (Red Haven and Sun High) and three cherry (Regina, Skeena and Selah) cultivars grown at the AHS Jr AREC, Winchester. Preliminary results confirmed the effects of ethephon in delaying bloom date in peach, and such effects were dependent on application timing and concentration (Figure 2). Transcriptomic analyses and hormonal profiling will be also performed on buds treated with ethephon to quantitatively characterize hormones, hormonal pathways and molecular networks that are altered by exogenous ethephon applications during bud dormancy.
Link to Liu and Sherif, Frontiers in Plant Science https://pubmed.ncbi.nlm.nih.gov/31620159/
For the list of references cited, refer to the paper published by Liu and Sherif, 2019, at Frontiers in Plant Science, https://www.frontiersin.org/articles/10.3389/fpls.2019.01408/full